It looks that way. Twenty to 30 years ago, surveys suggested 10 to 15 percent of Americans had tried it at least once. Five to 10 percent had engaged occasionally in BDSM—an umbrella term for bondage, dominance/submission, and sadomasochism. Fewer embrace it as a lifestyle or identity: Even in big cities, attendance at BDSM conventions is said to be only 1,500 to 2,000. But in the last year, the Fifty Shades of Grey trilogy has sold more than 65 million copies. The membership of FetLife, a social networking site for BDSM enthusiasts, has doubled to nearly 2 million. Sales of books and equipment have increased. So has attendance at BDSM events. BDSM-related Internet searches (domination, master, sex slave, sadism) went up 70 to 80 percent. College groups devoted to “kink,” largely BDSM, gained official recognition at Tufts and Harvard…